This invention relates to molded thermoplastic articles in continuous strip form and to methods and apparatus for molding such articles. The embodiment of the invention described herein comprises a continuous strip of plastic housings for electrical connectors. However, it will be apparent that the principles of the invention can be used to produce many other plastic articles in continuous strip form.
Application Ser. No. 734,708 discloses and claims a continuous strip of molded thermoplastic electrical connector housings comprising a carrier strip from which the housings extend at spaced-apart intervals. Each housing has a cavity extending therethrough transversely of the length of the strip, these cavities being dimensioned to receive electrical contact terminals. Each housing has a wire-receiving end through which the stripped end of a wire can be inserted into the cavity to position the metallic core of the wire in the wire barrel portion of the terminal with the end portion of the insulation of the wire disposed in the housing at the wire-receiving end thereof. An intermediate portion of the housing is crimped and the compressive crimping forces are transmitted through the thermoplastic material to the wire barrel portion of the terminal to effect crimping of the terminal onto the wire. A portion of the housing at the wire-receiving end is also crimped onto the insulation of the wire to compress the housing into constrictive embracing relationship with the insulation thereby to provide some sealing effect and preferably, a strain relief for the wire so that when a tensile force is applied to the wire, the tensile force will not be transmitted to the crimped connection between the wire core and the wire barrel portion of the electrical terminal in the housing. Contact terminal devices in accordance with the teachings of Application Ser. No. 734,708 have been enthusiastically received in the electrical industry and are gaining widespread acceptance.
Connecting devices of the type shown in application Ser. No. 734,708 have heretofore been made with a commonly used thermoplastic material, 6--6 nylon polyester. This material has properties (such as strength, hardness, and dielectric strength which are well suited for most portions of the connector housing and this material will withstand crimping forces without fracture. The housing can thus be crimped onto the wire and the forces required to crimp the wire barrel portion of the terminal in the housing onto the wire will not cause cracking of the insulating housing. Many thermoplastic materials, including 6--6 nylon polyester, have a tendency to relax after they are permanently deformed, that is, after they are crimped, and while this relaxation may be unobjectionable under many circumstances, it does prevent the achievement of an extremely high quality crimped connection between the plastic housing and the insulation of the wire; in other words, the relaxation of the plastic detracts from the effectiveness of the insulation supporting crimp. As a result, sealing and a good strain relief between the wire and the housing are not obtained. Thus, housings in accordance with application Ser. No. 734,708 which are of conventional thermoplastic materials are satisfactory for most purposes although under some circumstances it would be desirable to have an improved insulation supporting crimp of the housing onto the wire for stain relief and sealing purposes.
In accordance with the teachings of the instant invention, electrical connector housings in continuous strip form are of two distinctly different, but compatible, thermoplastic materials, one of which has optimum properties for most portions of the electrical connector housing, those portions in which the contact terminal is contained, and the other of which has optimum physical properties for the portion of the housing which is crimped onto the insulation of the wire. Specifically, the portions of the housing which are crimped onto the wire insulation are of a material which, upon such deformation as takes place during crimping, remains permanently in its deformed condition and has no tendency to return to its original dimensions. The remaining portions of the housing are of material which has optimum properties as regards, for example, dielectric strength and hardness.
Continuous strip in accordance with the invention can be manufactured at extremely low cost and at very high production rates by injecting the two materials into mold cavities provided on the surface of a molding wheel while the molding wheel is rotating and the surface is moving past the nozzle of the injection molding apparatus. When the two materials are injected at spaced-apart locations into the mold cavities, the materials rapidly fill each cavity and the two fronts of the material meet and merge with each other to form a boundary zone in each of the molded articles. On one side of this boundary, the article or connector housing will be composed of the first material and on the other side it will be composed of the second material.
It is accordingly an object of the invention to provide an improved method of molding thermoplastic materials. A further object is to provide a method of producing endless strip of thermoplastic articles in side-by-side relationship with each article being composed of two different materials which are separated by a boundary zone. A further object is to provide a continuous strip of thermoplastic articles, each article comprising two separate thermoplastic materials. A further object is to provide an improved electrical connector housing in endless strip form. A further object is to provide an improved electrical connecting device which can be crimped onto the stripped end of a wire.